Power electronics devices employ electronics packages (devices) that generally contain electrical circuitry for conducting electrical current which, in turn, generates thermal energy (i.e., heat). Automotive high-power electronics, such as those employed in electric and hybrid-electric vehicles typically generate a significant amount of thermal energy during operation. Excessive heat build-up may cause reduced performance including electrical circuit failure. Thus, thermal energy must be dissipated and transferred away from the electronics to ensure proper operation of the assembly. Additionally, the power capability of the electronics package(s) and size of the electronics assembly generally depend upon the amount of heat dissipation that may be achieved.
For very high-power applications, such as electronics packages used in hybrid-electric or electric vehicles, enhanced cooling of electronics may be required. U.S. Pat. No. 6,639,798 discloses an automotive electronics heat exchanger employing a heat sink device having a fluid vessel in fluid communication with an automotive radiator. The heat sink device is positioned in thermal communication with one side of an electronics power package such that fluid coolant flows through the heat sink device to cool the electronics package. The entire disclosure of U.S. Pat. No. 6,639,798 is hereby incorporated herein by reference.
When orienting the electronics package(s) relative to the heat sink device, conventional assembly approaches generally suffer in that the distance between the heat sink device and the cooling surface of the power electronics package(s) is variable. This variability in distance between discrete power packages and the heat sink device can adversely affect the thermal performance of the power electronics assembly.
Discrete electronics packages are typically wave soldered onto the circuit board. The height of the cooling surface of the discrete power packages with respect to the circuit board generally varies due to process variations and material tolerances. Placing a heat sink (e.g., rail) with a thermal interface material onto the cooling surface of the discrete power package(s), at this stage of the process, generally creates a variable bond line for the thermal interface material. This variable bond line may cause large thermal losses in the power electronics stack which results in less effective cooling. The power stack in a typical assembly is generally defined as the material layers between the circuit board substrate (die) and the cooling fluid, which may include the die, solder, direct bond copper aluminium nitride (AlN), thermal interface material, and heat sink device (rail) with coolant.
Conventional mechanical methods of forcing the discrete power package(s) against the heat sink, once it has been soldered onto the substrate to reduce these variations, typically produce large amounts of stress and deformation in the power package leads. Additionally, applying force generally requires the addition of a spring or durometer material in conjunction with a hole, to be placed in the circuit board. Further, if a grease or adhesive is used between the heat sink device and the discrete power packages, the variable bond line can produce excess material that flows onto other areas of the assembly, possibly causing electrical shorts.
It is therefore desirable to provide for an enhanced electronics assembly that minimizes thermal losses in the power stack for electronics package(s) mounted onto a substrate in thermal communication with a heat sink device. In particular, it is desirable to control package height variability between electronics package(s) and the heat sink device to achieve a cost affordable and enhanced cooling of electronics, such as those employed in high-power electronics packages on an automotive vehicle.